Neuronal activity reflecting progression of trials in the pre-supplementary motor area of macaque monkey: an expression of neuronal flexibility.

We studied the activity of single neurons in the pre-supplementary motor area (pre-SMA) of macaque monkeys as they performed two visuomotor tasks, called the visual fixation task and the visual fixation-blink task. Both tasks involved a sequence of three visual stimuli, red followed by yellow and green. The tasks differed in that the latter one had a gap within the period of the red stimulus, called a "blink". The tasks were performed in two modes, one of which included movements of both the arm and eye and the other of which involved only eye movements. In the arm-eye mode, the monkeys had to press a bar and fixate the red stimulus that appeared after bar press. To receive a reward, both the bar press and visual fixation had to be maintained until the green stimulus triggered bar release. In the eye mode, bar press and bar release were eliminated from the task. Of the 42 neurons active during the visual fixation task, 15 showed task-related activity in both arm-eye and eye modes, and our analysis focused on these cells. We found that the introduction of the blink in visual fixation-blink task abolished the task-related activity of these cells over the course of 2-4 trials. This finding suggests a role for the pre-SMA in reflecting progression of trials as an updating of motor instruction.